Shaving apparatus

ABSTRACT

Shaving apparatus with at least one cutting unit ( 3 ) having an outer cutter ( 4 ) and an inner cutter ( 6 ) which is rotationally drivable with respect to the outer cutter by means of an driving shaft ( 18 ) of a driving device, which driving shaft exerts a prestress force (FY) on the inner cutter in the direction of the outer cutter. During cutting of a hair, the hair exerts a cutting force (FR) on the inner cutter ( 6 ), which force has a direction that is opposite to the driving force (FD) for driving the inner cutter. Claimed is that the driving device comprises only one rotationally drivable coupling element ( 11 ) having at least one driving surface ( 12 ), that the driving shaft ( 18 ) bears axially ( 32,33 ) on the outer cutter ( 4 ) via said coupling element ( 11 ), and that the inner cutter ( 6 ) comprises at least one driven surface ( 13 ) cooperating with said driving surface ( 12 ) for exerting the driving force (FD), the direction of the driving force (FD) being substantially perpendicular to the driving surface ( 12 ) and the driven surface ( 13 ).

The invention relates to a shaving apparatus with a housing and at leastone cutting unit which can be pivotably and resiliently pressed in withrespect to the housing, said cutting unit comprising an outer cutter andan inner cutter that can be driven into rotation with respect to theformer, said inner cutter being provided with cutting elements withcutting edges, while said outer cutter is provided with hair trapopenings bounded by cutting edges for cooperating with the cutting edgesof the cutters for the cutting of hairs, wherein during cutting of ahair a cutting force is exerted by the hair on the inner cutter, and aplane through the totality of cutting edges defines a cutting plane,said shaving apparatus being further provided with a drive device havinga drive shaft for driving the inner cutter, which drive device duringcutting of a hair exerts a drive force on the inner cutter, while thedrive shaft exerts a prestress force in the direction of the outercutter.

Such a shaving apparatus is known from U.S. Pat. No. 4,192,065(=PHN8395). A so-termed cutting clearance which is as small as possibleshould be present between the cooperating cutting edges of the internaland the outer cutter for a satisfactory cutting of hairs. This has beenrealized in practice until now in that the drive shaft for driving theinner cutter is made resilient also in the direction of the outercutter. As a result, the inner cutter lies against the outer cutterunder a certain prestress, i.e. the cutting edges of the inner cutterare pressed with a certain force against the cutting edges of the outercutter. The cutting clearance accordingly is substantially zero. This isnecessary because during cutting of a hair the inner cutter isdecelerated, and the occurring cutting forces have a direction such thatthe cooperating cutting edges tend to be pressed apart somewhat, whichcould lead to too wide a cutting clearance. The resilient force of thedrive member prevents the clearance between the cutting edges becomingtoo great during cutting. As a result, the contact pressure between theinternal and the outer cutter is small during cutting of a hair, and thefriction is accordingly slight. In those periods in which no hairs arecut, however, the prestress force causes a comparatively great contactpressure between the cooperating cutters, and accordingly acomparatively high friction. Hairs are actually cut during less than 10%of the total shaving time during a normal shaving operation. In theremaining time the cutting edges bear on one another under the springpressure. This causes a friction for a major portion of the time, whichnot only causes wear of the cutting edges, but most of all consumes muchenergy. This means in the case of rechargeable shavers that thebatteries have to be recharged more often. Rechargeable batteries alsohave a finite life span, and the batteries will become incapable ofsatisfactory recharging after a certain time, so that they have to bereplaced. A lower friction between the cutters means that the apparatuswill use less energy. To reduce this friction, U.S. Pat. No. 4,192,065proposes to couple an auxiliary mass to the inner cutter, such that theauxiliary mass and the inner cutter are movable with respect to oneanother. The cutting force is obtained from the auxiliary mass duringcutting of a hair, the mass inertia supplying the driving force for theinner cutter. The driving force is transferred to the inner cutterthrough a sloping contact surface either of the auxiliary mass or of theinner cutter. As a result, the driving force is approximately parallelto the cutting force. The prestress force may then be chosen to be aminimum. A disadvantage of this construction is that the device fordriving the inner cutter is split up into two drive parts, i.e. thedrive shaft with its rectangular cam fitting in the rectangular openingof the inner cutter by means of which the driving force is suppliedduring the periods that no hairs are cut on the one hand, and on theother hand the auxiliary mass which is driven by the driven inner cutterand by means of which the driving force is supplied during cutting of ahair. A disadvantage of this known construction is that severalcomponents are necessary for driving the inner cutter, which renders theconstruction complicated and causes more wear of the components. Anotherdisadvantage is that the transmission of force from the auxiliary massto the inner cutter during cutting of hairs causes a high intermittentcontact pressure which leads to major wear. A yet further disadvantageis that the spring pressure at least necessary for bringing the innercutter into contact with the outer cutter again immediately aftercutting of a hair is supplied by the resilient drive shaft.

It is an object of the invention to provide a shaving apparatus in whichthe disadvantages mentioned above are avoided and in which the contactpressure between the cutters is a minimum both during cutting of hairsand during periods in which no hairs are cut.

The shaving apparatus according to the invention is for this purposecharacterized in that

-   -   the drive device comprises only one coupling member that can be        driven into rotation and that is provided with at least one        driving surface,    -   the drive shaft is axially supported on the outer cutter by        means of the coupling member, and    -   the inner cutter is provided with at least one driven surface        cooperating with the driving surface for exerting the driving        force on the cutter, the direction of said driving force being        substantially perpendicular to the driving surface and the        driven surface.

Owing to these measures, only few components are necessary for drivingthe inner cutter, and the force transmission takes place through contactsurfaces, which makes the contact pressure small. The axial resilientsupport or bearing obtains exclusively between the drive shaft and theouter cutter now, so that the resilient force of the drive shaft has noinfluence on the friction between the internal and outer cutters. Theforce transmission from the coupling member to the inner cutter takesplace through one or several cooperating driving or driven surfaces in adirection substantially perpendicular to these surfaces. In this manner,the force occurring during cutting of a hair and pressing the cuttersaway from one another is compensated by a force component of the drivingforce. The driving force becomes temporarily greater during cutting of ahair. The driving force is comparatively small in periods in which nohairs are cut. Since the driving force exerted on the driven innercutter is directed towards the outer cutter at an angle, thecomparatively small driving force causes only a small contact pressurebetween the cutters, and accordingly a low friction.

In a preferred embodiment, the shaving apparatus is provided withadditional means which cause a small contact pressure between thecutters so as to prevent a cutting clearance from arising neverthelessduring the operation of the shaving apparatus, i.e. both during cuttingof hairs and in periods in which no hairs are cut. As a result, theinner cutter will always bear on the outer cutter. A further advantageof a slight contact pressure between the cutters is that this contactcauses a self-sharpening effect of the cutting edges, so that thecutting system is wear-adaptive, i.e. the cutters remain in contact withone another also in the case of wear of the cutters, in particular ofthe inner cutter.

A preferred embodiment of a shaving apparatus according to the inventionis characterized in that the driving surface and the driven surfacecooperating therewith have mutually corresponding helical shapes.Helical surfaces remain in full contact with one another also if thecutters are pressed away from one another in axial direction, so thatthe planar pressure remains low.

A practical embodiment of a shaving apparatus according to the inventionis characterized in that the inner cutter has a carrier for the cuttingelements, which carrier is provided with the driven surfaces, in that acoupling member is present which is coupled to said carrier, the carrierbeing movable in axial direction with respect to the coupling member,while said coupling member can be coupled to the drive shaft and isprovided with the driving surfaces, and in that the means for obtaininga small contact pressure between the cutters are present between thecarrier and the coupling member.

A further embodiment of the shaving apparatus mentioned above ischaracterized in that said means are formed by at least one compressionspring.

Another embodiment of the shaving apparatus mentioned above ischaracterized in that said means are formed by centrifugal elements, forexample balls, which are enclosed between a pressure surface of thecarrier and a surface of the coupling member that is directed radiallyoutwards and obliquely towards the carrier. The rotary movement causes acentrifugal force to be exerted on the balls. Owing to the slopingsurface, the balls are pressed both radially outwards and in a directiontowards the carrier, whereby the inner cutter is pressed against theouter cutter. This contact pressure is meant to keep the cutting edgesof the cutters against one another by a small force during those periodsin which no hairs are cut, while only a slight friction is causedbetween the cutters.

The moment a cutting edge of the driven cutter encounters a hair, thecutting force will increase because this cutting force is to cut throughthe hair. Immediately after the hair has been severed, the cuttingelement, and accordingly the cutter, shoots through a short distance andthus becomes disengaged from the driving member for a short time. Iother words, the driven surface becomes detached from the drivingsurface, viewed in tangential direction. The driven inner cutter thenexperiences no force in the direction of the outer cutter until themoment the surfaces come into contact again, which may last a fewmilliseconds. If the inner cutter is obliged to cut another hair duringthis period, a cutting clearance would arise between the cutters owingto the cutting force arising, because there is no counter force. Theforce of the balls mentioned above is too small to prevent this. Toprevent this shooting-through of the driven cutter, the movement of thecutter must be damped immediately after cutting of a hair. The shavingapparatus is for this purpose characterized in that the coupling memberis provided with a cam, and the pressure surface of the carrier isdirected obliquely towards the coupling member viewed in a directionopposed to the drive direction, such that the ball lies enclosed betweensaid cam and the sloping pressure surface. Immediately after cuttingthrough of a hair, the ball should run up against this sloping portionof the pressure surface, which is possible only if the ball can moveradially in inward direction. However, the centrifugal force acting onthe ball prevents this. The ball accordingly remains against the cam, sothat the driving surface remains against the driven surface.

Yet another embodiment of the shaving apparatus according to theinvention is characterized in that the means for obtaining a smallcontact pressure between the cutters comprise a spring which causes atorque action between the coupling member and the inner cutter, wherebythe helical driving surface is held against the cooperating helicaldriven surface. The torque keeps the driving surfaces against the drivensurfaces, also in those periods in which no hairs are cut. The helicalshape of the surfaces ensures that a small force is exerted on the innercutter in the direction of the outer cutter, so that a small contactpressure always remains between the cutting elements of the cutters.

The invention will now be explained in more detail below with referenceto an embodiment shown in a drawing, in which

FIG. 1 shows a shaving apparatus with three cutting units in perspectiveview,

FIGS. 2 and 3 diagrammatically show the forces exerted on the innercutter during cutting of a hair and during periods in which no hairs arecut,

FIG. 4 diagrammatically shows an example of the drive of an inner cutterof a rotary shaving apparatus according to the invention,

FIG. 5 is an exploded perspective view of a first embodiment of thedrive of an inner cutter of a rotary shaving apparatus according to theinvention,

FIG. 6 is an exploded elevation of the drive of the inner cutter of FIG.5,

FIG. 7 shows the lower side of the coupling member of FIG. 5 inperspective view,

FIG. 8 is a cross-sectional view of the drive of FIG. 5,

FIG. 9 is a diagrammatic two-dimensional picture of the drive of FIG. 8taken on the line IX-IX,

FIGS. 10 a to g are exploded perspective views of a second embodiment ofthe drive of an inner cutter of a rotary shaving apparatus according tothe invention,

FIG. 11 is a cross-sectional view of the drive of the inner cutter ofFIG. 10, and

FIG. 12 is a diagrammatic two-dimensional view of the drive of FIG. 4taken on the line 12-12.

Corresponding components have been given the same reference numerals inthe description of the ensuing embodiments.

FIG. 1 shows a rotary shaving apparatus with a housing 1 and a shavinghead holder 2 which can be removed from the housing and/or is hinged tothe housing. Three cutting units 3, also denoted shaving heads, arepresent in the shaving head holder, each comprising an outer cutter 4with hair trap openings 5 and an inner cutter 6 that can be driven intorotation with respect to the outer cutter. The inner cutters are drivenin a known manner by a motor (not shown) present in the housing of theshaving apparatus.

FIG. 2 shows the forces that occur during cutting of a hair 7 whichprojects through a hair trap opening 5 of the outer cutter 4. Rims ofthe hair trap openings are provided with cutting edges 8. Referencenumeral 9 denotes a cutting element of the driven inner cutter 6. Eachcutting element 9 has a cutting edge 10 for cooperation with the cuttingedge 8 of the external, usually stationary cutter 4. The plane throughthe total of cutting edges is defined as the cutting plane C_(S). Thisis the plane in which the hair is to be cut through. The movement of thecutting element 9 is indicated by an arrow M and is parallel to thecutting plane C_(S). The cutting element 9 is driven by a couplingmember 11 which is provided with a driving surface 12. The cuttingelement 9 has a driven surface 13 for cooperation with the drivingsurface 12. The drive is depicted diagrammatically. In a practicalembodiment, a coupling member usually does not drive each cuttingelement separately, but instead drives the entire inner cutter 6, aswill become apparent from further examples below.

When a cutting edge 8 of a cutter hits against a hair 7 so as to cut itthrough, a force F_(R) is exerted on the cutting element by the hair,which force encloses an angle α with the cutting surface C_(S) and has adirection such that the cutting element of the outer cutter 4 is pressedaway (in the negative y-direction). The component of the force in they-direction is referenced F_(Ry). Without further measures, a cuttingclearance C_(G) would arise during cutting as a result of this, which isdetrimental to the cutting process because the cutting forces willbecome greater, and in addition an unpleasant pulling action would beperformed on the hair, especially if the clearance becomes too great.According to the invention, the direction of the driving force F_(D)exerted by the coupling member 11 on the cutting element 9 isapproximately parallel to the direction of the force F_(R) exerted bythe hair 7 on the cutting element 9. This driving force F_(D) isaccordingly perpendicular to the driving surface 12 and the drivensurface 13 and also encloses approximately an angle α with the cuttingsurface C_(S). The component of the driving force F_(D) in they-direction, indicated by the arrow F_(Dy), now compensates the forceF_(Ry), so that the cutting edges 8, 10 of the cutters 4, 6 remainagainst one another as much as possible, and no or at most a very smallcutting clearance C_(S) arises during cutting.

FIG. 3 shows what forces act on the inner cutter in the periods in whichno hair is cut. There is accordingly no reaction force of a hair on thecutting element 9. The force F_(D) exerted by the coupling member 11 onthe cutting element 9 so as to move the cutting element in the directionM is only small. It is mainly frictional forces that have to beovercome. This means that also the component F_(Dy) of the driving forcein the y-direction is small, i.e. the cutting element 9 is pressed inthe direction of the outer cutter 4 with a small force. Theperpendicular force F_(N) between the internal cutting element 9 and theouter cutter 4 is accordingly also small, and thus the frictional forceF_(F) will be small. It is accordingly achieved by the invention thatthe friction between the cutters is as small as possible both duringcutting of a hair and in the periods in which no hairs are cut. Theabove situation holds not only for shaving apparatuses with rotarycutting elements, but also for shaving apparatuses with reciprocatingcutting elements. The direction of the reaction force F_(R), i.e. theangle α, depends inter alia on the wedge angle β of the cutting element9. The wedge angle is the angle enclosed by the cutting surface C_(S)and the leading surface 9 a, seen in the direction of movement M, of thecutting element 9. The wedge angle β lies between 40° and 50° in arotary shaving apparatus, and the angle α on average between 17.50 and20°. For shaving apparatuses with reciprocating cutting elements, thewedge angle β is 90° or almost 90°, which makes the angle α muchgreater.

FIG. 4 diagrammatically shows a simple embodiment of the rotary drive ofa shaving apparatus. A rotary driven inner cutter 6 is built up from acircular carrier 14 provided with a central coupling bush 15 and anumber of cutting elements 9 with cutting edges 10. The outer cutter 4has the shape of a circular cap with a U-shaped groove 16 and a largenumber of lamellae 17 that extend approximately in radial directions(see also FIGS. 1 and 2). Between the lamellae there are the slottedhair trap openings 5 bounded by cutting edges 8 of the lamellae. Theinner cutter 6 is placed in the cap-shaped outer cutter 4 such that thecutting elements 9 lie in the groove 16 and the cutting edges 8 and 10cooperate with one another. The inner cutter is driven by a drive shaft18 provided with a coupling member 11. This drive element has a numberof helical surfaces 12 which make contact with similar helical drivensurfaces 13 of the coupling bush 15 of the internal cutting element 9.The helical shapes of these surfaces cause a driving force F_(D) to beexerted on the inner cutter, which force encloses an angle α with thecutting surface C_(S) and has a direction such that the inner cutter 6is forced towards the outer cutter 4. In fact, the coupling member 11exerts a torque on the cutter 6, in which F_(D) represents the couplingforces which have a tangential direction and enclose an angle α with thecutting surface C_(S). The coupling member 11 is axially supported onthe outer cutter 4 and is for this purpose provided with a bearingsurface 32, while the outer cutter has a counter-bearing surface 33.

It will be obvious that the reaction force F_(R) exerted on the cuttingelement by a hair to be cut during cutting of this hair is not alwaysthe same, but varies somewhat in dependence inter alia on the type ofhair and the sharpness of the cutting edges. It is also necessary toprevent as much as possible that a cutting clearance C_(G) arises, notonly during cutting of a hair, but also during periods in which no hairis cut. It is important, therefore, that the inner cutter 6 isnevertheless pressed in the direction (y-direction) of the outer cutter4 by a small force. For this purpose, a spring 19 is provided between apressure plate 20 of the drive member 18 and the bush 15 of the innercutter in the example of FIG. 4, exerting a small spring pressure on theinner cutter. This force is indicated by the arrow F_(y) in FIG. 3.

A more practical example of a rotary drive of the inner cutter is shownin FIGS. 5 to 7. The inner cutter 6 has a number of cutting elements 9.The cutter is fastened to a circular carrier plate 14. A synthetic resincoupling bush 15 is fastened in a central opening 21 of the carrierplate. A drive member in the form of a drive shaft 18 is driven intorotation by a motor (not shown). The drive shaft 18 has a profiledcoupling head 22. A coupling member 11 is present between the driveshaft 18 and the coupling bush 15 for driving the inner cutter 6. Thecoupling member is axially supported on the outer cutter 4 and is forthis purpose provided with a bearing surface 32, while the outer cutterhas a counter-bearing surface 33 (see FIG. 8). The coupling member isprovided with a profiled cavity 24 into which the coupling head 22 fits.The coupling member is driven into rotation by the drive shaft in thismanner. The coupling member 11 is fastened against the lower side of thecoupling bush 15/inner cutter 6 by means of snap hooks 25. The somewhatcup-shaped coupling member 11 has three elevations 23 which form thedrive elements. Each elevation 23 has a helical drive surface 12. Thecoupling bush 15 is also provided with three elevations 26. Theseelevations are clearly visible in FIG. 7, which shows the lower side ofthe coupling bush 15. Each elevation has a driven surface 13. Eachdriving surface 12 cooperates with a corresponding driven surface 13.The surfaces 12 and 13 are of mating helical shapes. When the couplingmember 11 is driven in the direction of rotation M by the drive shaft18, the driving elevations 23 carry along the respective elevations 26of the coupling bush 15 and thus drive the inner cutter 6 into rotation.The helical driving surfaces 12 lie against the associated helicaldriven surfaces 13 during this (see FIG. 9). The force transmissiontakes place perpendicularly to the respective surfaces, as is indicatedby the arrow F_(D), and is approximately parallel to the reaction forceF_(R) exerted by the hair 7 on the cutting element 9, and accordingly onthe inner cutter 6, during severing of the hair.

Three balls are present between the coupling member 11 and the couplingbush 15, regularly distributed over the circumference. The balls 27 areeach present in a chamber 28 between the elevations 26 and are enclosedbetween a sloping surface 29 of the coupling member 11 and a surface 30of the coupling bush 15 (see FIG. 8). When the coupling member and thecoupling bush rotate along with the inner cutter, the balls 27 arepressed radially outwards against the sloping surface 29 by thecentrifugal force. This also presses the balls upwards against thesurface 30 of the coupling bush 15, thus pressing the inner cutter 6upwards against the outer cutter 4 (see FIG. 8). This force F_(y) isonly small and serves to ensure that the cutting edges of the cuttersremain against one another during periods in which no hairs are cut. Thefriction between the cutters 4 and 6 is only small.

The driving force F_(D) is only small during periods in which no hairsare cut. This force (in fact a torque in the case of rotary shavingapparatuses) merely serves to keep the inner cutter rotating and toovercome the small friction between the cutters. The driving force F_(D)increases during cutting of a hair. The inner cutter then experiences agreater force F_(D) and is as it were prestressed. The moment the hairis cut through, the reaction force F_(R) exerted by the hair on theinner cutter (cutting element) disappears, with the result that thecutter shoots through owing to the driving force F_(D) and tends todetach itself from its drive, i.e. the driven surface 13 becomesdetached from the driving surface 12. There is no force present anymoreat that moment which keeps the cutters 4 and 6 against one another,except for the small centrifugal force of the balls. This is undesirablebecause it is possible that a hair is about to be cut again immediatelyafter this, which could give rise to a cutting clearance C_(G). Toprevent this, the surface 30 of the coupling bush 15 against which theball 27 rests is somewhat sloping with respect to the direction ofmovement M (by approximately 10°), viewed in a direction opposed to thedirection of movement M. The ball 27 lies between the cam-type driveelement 11 and the sloping surface 30. As was explained above, thecoupling bush 15 (with the cutter 6) tends to shoot through with respectto the coupling member 11 the moment a hair has been cut through, andalso with respect to the ball 27. The sloping surface 30 should now runup against the ball 27, while the distance between the surface 29 andthe sloping surface 30 becomes smaller, i.e. smaller than the balldiameter. The ball could indeed move radially inwards and downwards (seeFIG. 9), but the centrifugal force exerted on the ball prevents this.The ball remains against the drive element 11 and thus prevents thecoupling bush 15 with the cutter from shooting through. The drivingsurfaces 12 accordingly remain pressed against the corresponding drivensurfaces 13, so that the inner cutter remains against the outer cutter.There will be no cutting clearance immediately after cutting through ofa hair.

Another practical example of a rotary drive of the inner cutter is shownin FIGS. 10 to 12. Components similar to those of the example of FIGS. 5to 9 have been given the same reference numerals. The inner cutter 6(FIG. 10 a) has a number of cutting elements 9. The cutter is fastenedon a circular carrier plate 14 (FIG. 10 c). A synthetic resin couplingbush 15 is fastened in a central opening 21 of the carrier plate. Adrive member in the form of a drive shaft 18 (FIG. 10 e) is driven intorotation by a motor (not shown). The drive shaft 15 has a profiledcoupling head 22. A coupling member 11 (FIG. 10 d) is present betweenthe drive shaft 18 and the coupling bush 15 for driving the inner cutter6. The coupling member is axially supported on the outer cutter 4 and isfor this purpose provided with a bearing surface 32, while the outercutter has a counter-bearing surface 33 (see FIG. 11). The couplingmember is provided with a profiled cavity 24 into which the couplinghead 22 fits. The coupling member is driven into rotation by the driveshaft in this manner. The somewhat cup-shaped coupling member 11 isprovided in its interior with three elevations 23 which form the driveelements. FIG. 10 f shows the interior of the coupling member 11, i.e.FIG. 10 f is FIG. 10 d turned upside down. Each elevation 23 has ahelical driving surface 12. The coupling bush 15 (FIG. 10 c) also hasthree elevations 26. Each elevation has a driven surface 13. Eachdriving surface 12 of the coupling member 11 cooperates with anassociated driven surface 13 of the coupling bush 15. The surfaces 12and 13 are of mating helical shapes. When the coupling member 11 isdriven in the direction of rotation M by the drive shaft 18, the drivingelevations 23 carry along the respective elevations 26 of the couplingbush 15 and thus drive the inner cutter 6 into rotation. The helicaldriving surfaces 12 bear on the associated helical driven surfaces 13(see also FIG. 12) during this. The force transmission takes placeperpendicularly to the surfaces, as is indicated by the arrow F_(D), andis approximately parallel to the reaction force F_(R) exerted by thehair 7 on the cutting element 9, and accordingly on the inner cutter 6,during cutting through of the hair.

The driving force F_(D) is only small in periods in which no hairs arecut. This force (in fact a torque in the case of rotary shavingapparatuses) merely serves to keep the inner cutter rotating and toovercome the small friction between the cutters. The driving force F_(D)increases during cutting of a hair. The inner cutter then experiences agreater force F_(D) and is as it were prestressed. The moment the hairhas been cut through, the reaction force F_(R) exerted by the hair onthe inner cutter (cutting element) disappears, so that the cutter shootsthrough owing to the driving force F_(D) and tends to detach itself fromits drive, so that the driven surface 13 becomes detached from thedriving surface 12. No force is present anymore at that moment whichkeeps the cutting edges 8 and 10 of the cutters 4 and 6 against oneanother. This is undesirable because it is possible that a hair is aboutto be cut immediately afterwards, with the result that a cuttingclearance C_(G) could arise. To prevent this, a torque is exerted on thecoupling member 11 by resilient elements, keeping the driving surfaces12 of the coupling member 11 against the cooperating driven surfaces 13of the coupling bush 15. The inner cutter 6 is for this purpose providedwith an annular plate 34 from which three blade springs 35 are bent(FIG. 10 b). The annular plate 34 is present between the disc-shapedplate 36 from which the cutting elements 9 are formed (FIG. 10 a) andthe carrier 14 with the coupling bush 15 (FIG. 10 c). The blade springs35 project through openings 37 of the coupling bush 15, as is indicatedby a broken line in FIG. 10 c. The coupling member 11 is provided withthree studs 38 (FIG. 10 f) for cooperation with the three blade springs35. FIG. 10 g shows the assembly of the annular plate 34, the carrier14, and the coupling member 11 in a situation in which these componentsare upside down as compared with FIGS. 10 b, 10 c, and 10 d. FIG. 10 gclearly shows that each end 35 a of the blade springs 35 is in contactwith a stud 38. This contact is achieved with a certain, smallprestress, as is also shown in FIG. 12. Said prestress exerts a torqueon the coupling member 11 in the drive direction M. The driving surface12 is pressed against the mating driven surface 13 thereby. The drivingsurface 12 continues to lie against the driven surface 13 alsoimmediately after cutting of a hair. Since these surfaces 12 and 13 arehelical, it also has the result that a small force F_(y) in thedirection of the outer cutter 4 is exerted on the inner cutter 6. Thisachieves that the cutting elements 9 and 17 remain in contact with oneanother also immediately after cutting of a hair, so that no cuttingclearance arises. It is obviously also possible for the studs andelevations 38 and 23 to be one integral whole, i.e. the blade spring 35bears directly on the elevation 23. The blade springs 35 thus have thesame function as the centrifugal action of the balls 27 in theembodiment described above (and shown in FIGS. 8 and 9).

Such a shaving apparatus may also be provided with a hair-pulling memberas described in U.S. Pat. No. 4,545,120. A hair-pulling member comprisesa number of resilient hair-pulling elements which cooperate with thecutting elements such that a hair-pulling element first pulls up thehair over a small distance and only then does the cutting element cutthrough the hair. The hair is cut off closer to the skin as a result ofthis. Such a hair-pulling member may be integrated into the annularplate 34 in a simple manner. FIG. 10 b shows one such hair-pullingelement 39 with broken lines. FIG. 12 also shows a hair-pulling element39 bent from the annular plate 34.

1. A shaving apparatus with a housing and at least one cutting unitwhich can be pivotably and resiliently pressed in with respect to thehousing, said cutting unit comprising an outer cutter and an innercutter that can be driven into rotation with respect to the former, saidinner cutter being provided with cutting elements with cutting edges,while said outer cutter is provided with hair trap openings bounded bycutting edges for cooperating with the cutting edges of the cutters forthe cutting of hairs, wherein during cutting of a hair a cutting force(F_(C)) is exerted by the hair on the inner cutter, and a plane throughthe totality of cutting edges defines a cutting plane, said shavingapparatus being further provided with a drive device having a driveshaft for driving the inner cutter, which drive device during cutting ofa hair exerts a drive force (F_(D)) on the inner cutter, while the driveshaft exerts a prestress force in the direction of the outer cutter,characterized in that the drive device comprises only one couplingmember that can be driven into rotation and that is provided with atleast one driving surface, the drive shaft is axially supported on theouter cutter by means of the coupling member, and the inner cutter isprovided with at least one driven surface cooperating with the drivingsurface for exerting the driving force on the cutter, the direction ofsaid driving force being substantially perpendicular to the drivingsurface and the driven surface.
 2. A shaving apparatus as claimed inclaim 1, characterized in that means are present for obtaining a smallcontact pressure between the cutters.
 3. A shaving apparatus as claimedin claim 1, characterized in that the driving surface and the drivensurface cooperating therewith have mutually corresponding helicalshapes.
 4. A shaving apparatus as claimed in claims 2 and 3,characterized in that the inner cutter has a carrier for the cuttingelements, which carrier is provided with the driven surfaces, a couplingmember is present which is coupled to said carrier, the carrier beingmovable in axial direction with respect to the coupling member, whilesaid coupling member can be coupled to the drive shaft and is providedwith the driving surfaces, and the means for obtaining a small contactpressure between the cutters are present between the carrier and thecoupling member.
 5. A shaving apparatus as claimed in claim 4,characterized in that said means are formed by at least one compressionspring.
 6. A shaving apparatus as claimed in claim 5, characterized inthat said means are formed by centrifugal elements which are enclosedbetween a pressure surface of the carrier and a surface of the couplingmember that is directed radially outwards and obliquely towards thecarrier.
 7. A shaving apparatus as claimed in claim 6, characterized inthat the coupling member is provided with a cam, and the pressuresurface of the carrier is directed obliquely towards the coupling memberviewed in a direction opposed to the drive direction, such that thecentrifugal elements lie enclosed between said cam and the slopingpressure surface.
 8. A shaving apparatus as claimed in claim 4,characterized in that the means for obtaining a small contact pressurecomprises a spring which causes a torque between the coupling member andthe inner cutter, by means of which the helical driving surface is heldagainst the cooperating driven helical surface.
 9. A shaving apparatusas claimed in claim 8, characterized in that the spring is a bladespring bent in axial direction from a plate, said plate being fastenedto the inner cutter.
 10. A shaving apparatus as claimed in claim 9,characterized in that the plate is circular with hair-pulling elementsat its circumference, each such element lying against an associatedcutting element in front of said cutting element seen in the drivedirection.